JP2000239757A - Method and flux for refining molten aluminum alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove the gas and impurities at high removal level by adding alum flux to a molten aluminum alloy in which raw Al is melted. SOLUTION: Alum flux is formed of single alum, or through combination of alum with other flux such as potassium sulfate. Al alloy cast ingot having the composition consisting of <=0.25 cc/100 g Al H2, and <=200 ppm oxide including MgO, Al2O3, and spinel is melted in a melting furnace. Alum flux of 1-0.01 mass % to the molten Al alloy is blown together with the inert gas such as N2. The alum flux decomposes and emits Sox such as sulfate and So2 at the temperature of 700 deg.C of the molten Al alloy. The Sox gas takes in H2 gas in the molten metal in bubbles, and is afloat on the surface of the molten metal in a fugacious manner to remove H2 gas in the molten metal. The impurities in the molten metal are afloat on the surface of the molten metal due to the stirring effect and the floating effect of the generated Sox gas and the inert gas, and removed from the molten metal through the accelerated slag condition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for refining pure aluminum or aluminum alloy (hereinafter simply referred to as aluminum alloy, and aluminum is also simply referred to as Al) and a flux for refining molten Al alloy.

[0002]

2. Description of the Related Art As is well known, a wrought Al alloy such as a plate, a mold, a wire or a bar is formed by rolling (hot rolling, cold rolling), extruding, or forging a cast Al alloy ingot. It is manufactured by performing plastic working.

[0003] In the melting and casting steps of the ingot for wrought Al alloy, usually, the Al raw material is used in a melting furnace.
(Al ingots, scraps of Al alloy products, etc.) are melted and the components are adjusted to refine the molten Al alloy. This refining of molten Al alloy (hereinafter simply referred to as molten Al) refers to blowing chlorine gas into the molten metal or blowing chloride-based flux with an inert gas as a carrier gas to remove gas components such as hydrogen in the molten metal. This is a step of purifying the molten metal by performing degassing or inclusion slagging to remove slag from the surface of the Al molten metal. And these molten aluminum after refining,
The hot water is supplied to the mold from a melting furnace via a hot water gutter or the like, with or without a holding furnace. At this time, the molten metal during the transfer is supplied to the mold, for example, by removing oxide-based inclusions such as alumina by a filter provided in a transfer trough or a filter box immediately before the mold, and supplied to the mold.
Cast into alloy ingots.

[0004] Degassing such as H ₂ gas in the molten metal by the chlorine gas is carried out in the following mechanism. That is, Cl ₂ blown into the molten metal reacts with the molten Al to generate AlCl ₃ , and the generated AlCl ₃ sublimates from a solid to a gas at about 250 ° C., and is finer than the blown Cl ₂ gas bubbles. AlCl ₃ gas bubbles. Since the partial pressure of H ₂ gas in this AlCl ₃ gas bubble is almost zero, H ₂ gas in the molten metal diffuses and balances the partial pressure.
The AlCl ₃ gas bubbles move from the molten metal to the fine AlCl
₃ gas bubbles rise to the surface of the melt, by volatilization of, H ₂
Gas is removed from the melt.

[0005] In addition, de-inclusions such as inclusions in the molten metal are:
Such as the AlCl ₃ gas bubbles to less than inclusions adhere to inclusions from adhering to AlCl ₃ gas bubbles takes place by mutual adhesion between the inclusions of AlCl ₃ gas bubbles and the molten metal.

However, recently, due to problems such as the harmfulness of chlorine gas and the contribution to the generation of dioxins, chloride flux is replaced with an inert gas as a carrier gas in the Al molten metal instead of the chlorine gas. It has been used to promote blowing, degassing of molten metal and removal of slag.

Until that time, when chlorine gas is mainly used for refining such as degassing of H _{2 in} the molten metal and deintercalation, the flux used for this refining is used as a substitute for the chlorine gas, It has been used to promote the degassing of the molten metal or the removal of slag on the surface of the molten metal after the inclusions have been removed. In this slag, the oxide containing impurities generated by refining floats on the surface of the molten metal and exists as slag.The amount increases as the refining proceeds, and if left undissolved, this is re-dissolved or taken into the molten metal. , Because it may contaminate the molten metal,
This slag is removed from the molten metal or the melting furnace. As the flux for removing slag, for example, Japanese Unexamined Patent Publication No.
The -243136 discloses, mainly fluoride such as chloride and AlF ₃ such as KCl, was added 20 to 50 parts by weight sulfate and carbonates, such as potassium sulfate or nitrate, as a combustion improver for heating mixing A system flux and the like are disclosed. Japanese Patent Application Laid-Open No. 01-123035 discloses a mixed flux mainly composed of KCl, to which potassium sulfate, potassium nitrate and Al atomized powder are added as a combustion-promoting agent for heat generation.

[0008] The reason why these fluxes are a mixed system or a composite system containing the above-mentioned chloride is that the melting point of the chloride, which is the main component of the degassing process such as H ₂ gas in the molten metal and the refining process of the de-inclusions etc. This is because (decomposition temperature) is higher than that of the molten Al, and even if chloride alone is blown into the molten Al, it is difficult to decompose and the molten aluminum cannot be efficiently refined. Therefore, a method of lowering the melting point and easily decomposing in a molten metal as a mixed or composite compound obtained by adding the above-mentioned fluoride to chloride is adopted. In addition, a method is also adopted in which Al powder or the like is further added to generate heat so as to be easily decomposed in a molten metal.

[0009] Although these fluxes containing chlorides have less problems than chlorine gas, they still have the problem that chlorides are decomposed to generate chlorine gas. Therefore, non-halogen-based fluxes for refining have been required. I have. As this non-halogen refining flux, for example,
In the 207358 publication, potassium sulfate (K ₂ SO ₄ ) is mainly used,
A mixed flux in which a lithium (Li) to magnesium (Mg) compound for lowering the melting point of sulfate is added is disclosed.

In Japanese Patent Application Laid-Open No. 07-207358, potassium sulfate or lithium borate is used for dehydrogenation, but since the melting points of potassium sulfate and lithium borate are higher than the melting point of Al, the dehydrogenation reaction is gas- Proceed with a solid reaction,
We recognize that the reaction efficiency of dehydrogenation decreases. As a result, in order to lower the melting points of potassium sulfate and lithium borate, a mixed flux containing lithium sulfate, magnesium sulfate and the like is used. Then, the mixed flux whose melting point is lowered is melted in the molten metal to be in a liquid state, and the reaction with hydrogen in the molten metal proceeds as a gas-liquid reaction, and the generated hydrogen compound is gasified or removed as slag. Then, dehydrogenation is performed. Furthermore, in this conventional technique, when the mixed flux whose melting point has been lowered to about the temperature of the molten aluminum is blown into the molten metal using an inert gas as a carrier, melting of the flux at the tip of the blowing nozzle and clogging of the nozzle are prevented. Therefore, the preferable content of potassium sulfate is 60 to 99% by weight.

However, although this non-halogen-based refining flux certainly prevents the above-mentioned adverse effects due to the use of chlorine or chloride, it is important to remove degassed and deintercalated substances such as H ₂ gas in the molten metal. However, there is a problem that the refining efficiency of such a method is inferior to that of chlorine or chloride.

On the other hand, in the field of Al alloy products, for example, the surface properties (surface smoothness) of Al alloy materials in applications in the field of electronic and electrical components, such as disk substrates and printing plates for magnetic disks, and photosensitive drums. , Surface roughness) are becoming more and more severe. In addition, the demand for higher quality Al alloy products, such as higher strength, higher moldability, and higher corrosion resistance, for packaging containers such as cans, transport vehicles such as automobiles, and structural material applications is becoming increasingly severe. I have. Thus, with this, the need to further reduce impurities such as H ₂ or inclusions Al alloy ingot is increasing more and more.

[0013] On the other hand, the Al-dissolved raw material has been changed from a conventional aluminum ingot mainly to a scrap of an aluminum alloy product in accordance with social demands for establishing a recycling system for the aluminum alloy product scrap. It is getting. As a result, 100% scrap is used as the Al raw material. However, when the Al raw material is scrapped, an increase in the amount of impurity elements mixed from the scrap or gas components such as H ₂ is inevitable even if the scrap is pretreated. As a result, the use of Al alloy material product scrap as a melting raw material is limited to cast products, and some of the molten raw materials for wrought materials such as aluminum alloy plates and profiles such as rolling and extrusion are partially used. The fact is that it can only be used. Therefore, from the viewpoint of using the Al alloy material product scraps mainly of melting raw material for wrought material is also a need to further reduce impurities such as H ₂ or inclusions Al alloy ingot is increasing. Also, if this impurity reduction becomes possible,
The use of scrap aluminum alloy wrought scrap as a raw material for wrought aluminum alloy is of great social significance, such as the establishment of a complete recycling system for wrought aluminum alloy scrap.

However, in the field of refining Al alloys, non-halogen-based refining fluxes having the same refining efficiency as chlorine or chloride have not yet been put into practical use. However, in order to perform the degassing and the refining at a high reduction level of the inclusions, it is a fact that chlorine or chloride flux must be used in combination.

For this reason, the present inventors have disclosed in Japanese Patent Application No. 10-125978.
As a reference, a flux consisting of potassium sulfate alone was proposed as a refining flux for degassing and removing slag of molten Al. This technology does not use a mixed or composite system in which a compound that lowers the melting point of potassium sulfate, such as a compound of Li to Mg, is added as a flux composition, but a flux of potassium sulfate alone, degassing of Al molten metal and removal of inclusions. The main purpose is to perform refining at a high reduction level.

[0016]

However, even in this non-halogen flux, when an inert gas is blown into the Al melt as a carrier gas in order to apply to the actual refining of the Al melt, a slight amount of potassium sulfate is generated. There is a problem that it remains in the molten metal. That is, the refining ability itself of degassing potassium sulfate and removing inclusions is high. However, since the decomposition temperature or sublimation temperature of potassium sulfate is slightly higher than the temperature of the Al melt, some potassium sulfate blown into the Al melt remains in the melt without being decomposed.

If the potassium sulfate remaining in the molten metal is brought into the ingot, it becomes an inclusion and lowers the cleanliness and quality of the ingot. However, if the temperature of the molten metal is increased or the stirring time of the molten metal after the addition is increased, the remaining potassium sulfate is also decomposed, so that the remaining potassium sulfate can be eliminated.

However, in a series of steps of melting, refining, and casting an Al alloy, it is not possible to reduce or raise the temperature of the molten metal or not to shorten or lengthen the refining time from the viewpoint of cost reduction and energy saving. It is an issue. Therefore, since potassium sulfate has a problem of remaining in the molten metal, it is difficult to commercialize it as a flux for refining.

The present invention has been made in view of such circumstances, and an object of the present invention is to make it possible to perform refining capable of achieving a high level of degassing and deinclusion, An object of the present invention is to provide a non-halogen flux for refining Al and a method for refining molten Al alloy, which has no problem of remaining in the aluminum alloy.

[0020]

SUMMARY OF THE INVENTION In order to achieve this object, the gist of the method for refining molten Al alloy according to the present invention is as follows. Then, when casting an Al alloy, alum is used as the refining flux.

The gist of the flux for refining molten aluminum of the present invention is a refining flux for degassing and removing slag of molten aluminum for casting, wherein the flux is mainly composed of alum. (Corresponds to item 9).

The present inventors have sought a non-halogen-based refining flux that has a sublimation temperature lower than the temperature of the molten aluminum and has an excellent degassing and descaling effect. And
As a result, the color tone improvement and retention of foods such as moisture absorbents and pickles,
Or alum, which is widely used as a food additive for preventing discoloration, a photographic fixing agent, a leather tanning agent, a concrete admixture, a water purifying agent, a pharmaceutical, a cosmetic, a pigment, a deodorant, or an artificial jewel or a new ceramic, It has been found that the flux characteristics are satisfied.

That is, alum is represented by the general formula R ³ R ¹ (SO ₄ ) _2.
nH ₂ O (n = 12, 10, 6, 4, 3, 2, or 0) or R ¹ (R ³ (H ₂ O)
₆ ) (SO ₄ ) ₂・ nH ₂ O (n = 12, 10, 6, 4, 3, 2, 2 or 0) and a trivalent metal (R ³ ) and a monovalent metal (R ³ ) R ¹ ) is a generic term for double salts of sulfates. And, as the trivalent metal (R ³ ), Al, Fe, Cr, and as the monovalent metal (R ¹ ),
K, there is NH _4, Na. Among them, a typical one is AlK (SO
₄ ) ₂・ nH ₂ O (n = 12, 10, 6, 3, 2, 2 or 0) potassium alum or baked potassium alum, and AlNH ₄ (SO ₄ )
₂ · nH ₂ O (n = 12, 10, 6, 4, 3, 2, or 0) ammonium alum or baked ammonium alum. Of these, ammonium alum is thermally decomposed and oxidized
Since it becomes Al (Al ₂ O ₃ ), it is used for the artificial jewels and new ceramics.

This alum varies in type, but when heated, is heated to about 650 ° C. below the temperature of the molten aluminum alloy.
SO _X gas such as sulfurous acid gas (SO) or SO ₂ begins to decompose emitting from the vicinity of, the pyrolysis is completed in the vicinity of about 950 ° C., at the same time to produce an oxidized Al, it has the property that. Among these, when the heating temperature is between 400 and 550 ° C., for example, ammonium alum releases sulfate such as ammonium sulfate, and potassium alum releases sulfate such as potassium sulfate.

That is, the released sulfate and the decomposed and released sulfur dioxide gas have an effect of reacting with hydrogen in the molten metal to perform dehydrogenation. Melt temperature of the Al alloy is about 700 ° C., alum as an additive to blown flux in the molten metal, SO _X gas decomposition release, these sulfates such as sulfate or SO ₂ under this melt temperature Fume (fine particles) and SO
_X gas undergoes a solid-gas or gas-gas reaction with hydrogen in the molten metal. Then, it is possible to degas the molten metal by gasifying the generated hydrogen compound or separating and removing the hydrogen compound as slag from the molten metal. It also has the effect of purifying the molten metal by promoting slagging of inclusions and promoting slag removal for removing slag from the surface of the Al molten metal.

As a more specific operation, the produced SO _X
The gas rapidly diffuses into the Al melt due to the stirring effect of the inert gas, so that H ₂ gas in the melt is taken into the gas bubbles by diffusion and partial pressure equilibrium. Then, the fine SO _X gas bubbles float on the surface of the molten metal and volatilize, so that the H ₂ gas is removed from the molten metal. Also, inclusions in the molten metal, the stirring effect to floating effect of generating SO _X gas or an inert gas, floats on the melt surface from the melt, slag formation is removed from the molten metal is promoted.

Further, the generated fume is also rapidly diffused into the molten Al, thereby producing hydrogen and a hydrogen compound by a gas-solid reaction or melting and decomposing to produce SO.
_It generates _X gas and exhibits the same degassing and deintercalating effects as the generated SO _X gas. Therefore, the effect of removing gas components such as H ₂ gas and the like, particularly oxide-based inclusions in the molten metal increases due to the complex or synergistic action of these.

Further, the decomposed and released sulfates and SO _X gas have an excellent debris-removing effect as compared with conventional potassium sulfate and chloride fluxes. That is, as flux
When alum is used, the exothermic reaction oxidizes minute Al content in the slag, reduces the wettability between the Al molten metal and the slag on the surface of the Al molten metal, and has a debris removing effect to promote the separation of the two. This effect is further synergized to ensure a higher refining effect of the Al melt.

On the other hand, of the above-mentioned characteristics of alum, aluminum oxide (Al), which is to be a harmful impurity or inclusion in the molten metal, has a temperature of about 950 ° C. Therefore, since the formation temperature is sufficiently high with respect to the molten metal temperature of the Al alloy of about 700 ° C., Al oxide is rarely generated during the actual refining of the molten metal. In addition, the decomposition and release temperature of sulfate and SO _X gas was also about 700 ° C, as described above.
Because the temperature is sufficiently low compared to ℃,
Alum decomposes completely. Therefore, alum as flux added or blown into the molten metal,
Almost no aluminum oxide or sulfate remains in the molten metal. Further, even if the Al oxide is generated, the Al oxide is generated in the molten metal,
The particles are very fine compared to Al oxide generated when the molten metal comes into contact with the atmosphere. Accordingly, the stirring effect to floating effect of the generated SO _X gas or an inert gas, tends to rise to the surface of the molten metal from the molten metal, with slag formation is promoted, is removed from the molten metal by the skimming effect. As a result, the generated Al oxide hardly remains in the molten metal.

Therefore, alum as a flux has an excellent effect that it is possible to perform dehydrogenation and deintercalation of the molten metal without remaining in the molten metal.
However, ammonium alum, some refining conditions, the possibility of producing hydrogen NH ₄ is decomposed, to the hydrogen remaining in the melt, a long time of stirring with inert gas for removal of hydrogen There is also the possibility. Therefore,
It is most preferable to use potash alum or baked potash alum which does not have such a side effect. In addition,
In the present invention, in addition to the specific examples described above, among the compounds classified as alum, a compound having a refining action of releasing a sulfate or a sulfurous acid gas that performs dehydrogenation and generating no residual impurities harmful to the molten metal Are all included within the scope of the invention.

The present inventors have investigated the use of this alum. Although alum itself is widely used for the above various applications, it is used under a high temperature environment, as a flux, and in the refining of molten Al alloy. No examples were used. Many of the above-mentioned examples are intended to utilize the excellent properties of alum at room temperature as it is or to use it as a raw material for completely decomposing to obtain Al oxide. Therefore, from these technical ideas, the high temperature (during heating) characteristics of the alum, more specifically, the decomposition and release characteristics of sulfate and SO _X gas, which are intermediate products until completely decomposed to form Al oxide. Taking advantage of the part, the technical idea of using as a molten aluminum refining flux of Al alloy is unlikely to occur unless it is linked to the concept of molten aluminum refining of Al alloy, and therefore, there is no use example of alum related to the present invention. Inferred.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The significance of each requirement in the present invention will be described below.

In the present invention, the meaning that alum is used as a non-halogen refining flux and that the flux contains alum as a main component is not only a composition of alum alone (100%) but also a combination with another flux. Or it may be used as a mixture.

As described above, the alum flux of the present invention has functions and effects such as dehydrogenation of the molten metal, deintercalation and debris. Moreover, alum itself is cheaper than conventional fluxes. Therefore,
From these properties, alum alone may be used, but various fluxes in refining also have a role other than dehydrogenation and de-inclusions and slag removal of the molten metal.To satisfy these other properties, other fluxes are used. They may be used in combination or mixed.

Other fluxes include potassium sulfate (K ₂ SO ₄ ), sodium sulfate (Na ₂ SO ₄ ),
There are sulfates such as calcium sulfate (CaSO ₄ ) and ammonium sulfate, and carbonates and nitrates thereof. Further, there are chlorides such as KCl and fluorides such as AlF ₃ for dehydrogenation and deintercalation of molten metal. Further, there are a lithium (Li) to magnesium (Mg) compound such as an aluminum atomized powder or a nitrate such as potassium nitrate as a heat generating auxiliary agent, a lithium borate or the like for lowering a melting point of a sulfate, and the like. And these are added to the alum of the present invention,
As a flux composition, it can be used as a mixed flux with 10 to 90 wt% added. However, in order to prevent the generation of chlorine, the use of chloride such as KCl should be suppressed as much as possible.

The amount of the alum flux of the present invention to be blown into or added to the molten Al is determined from the required amount of refining such as the amount of degassing and the amount of inclusions of the molten Al and the amount of debris. In this respect, a product field of the Al alloy, electronic and electrical components field, transport fields such as automobiles, in order to correspond to the characteristics required of such structural material field, 0.25 cc of H ₂ of Al alloy ingot
/ 100gAl or less, magnesia (MgO), alumina (Al ₂ O ₃ ),
The total amount of oxides such as spinel (composite oxide of Al and Mg)
It is preferably at most 0 ppm (corresponding to claim 7).
Note that the total amount of oxides referred to in the present invention is the total amount of the three main oxides that are large in oxide and can be measured. The amount of the alum flux to be blown into the molten aluminum or the amount of the added alum flux for performing this level of refining is preferably 1 to 0.01 mass% with respect to the weight of the molten aluminum.
(Corresponding to claim 6). If the amount of the alum flux blown or added is less than 0.01 mass%, there is a possibility that degassing and inclusions cannot be achieved at the above-mentioned level. On the other hand, if the amount of alum flux blown or added exceeds 1 mass%, the refining effect is not improved, the refining cost is increased, and there is a possibility that the molten metal may be contaminated.

The addition of alum flux to the molten metal is as follows:
It is performed by blowing into the molten metal and adding (spraying) to the surface of the molten metal. The blowing method is the same as the usual blowing method for refining flux. That is, an alum powder is mixed with an inert gas such as N ₂ or Ar gas as a carrier from a nozzle or lance which is inserted into the Al melt at one end.
Blowing into the molten metal is preferable for refining efficiency.
3). The inert gas such as the N ₂ gas or the Ar gas plays an important role in agitating (bubbling) the molten metal together with the alum flux carrier to promote the refining action of the alum and the floating of the slag in the molten metal. Of course, stirring the molten metal
(Bubbling) In order to increase the effect, the molten metal may be stirred by blowing an inert gas during or after the blowing of the flux by using a lance different from the carrier gas or the same lance. Of course, in addition to the blowing, a mode of adding to the surface of the molten metal is also possible. In short, a preferable method for improving the refining effect can be appropriately selected.

The particle size or particle size of the alum powder is appropriately selected depending on the mode of addition to the molten metal. However, on the other hand, since alum has a hygroscopic property, it is preferable that the absorption of the flux does not hinder the operation of blowing or adding the flux, such as clogging of the flux blowing lance. In addition, when the alum that has absorbed moisture is used, moisture due to moisture absorption may be mixed into the molten metal, and may remain as harmful impurity hydrogen in the molten metal. In this regard, in order to use the alum in a dry state, it is preferable to use a means such as heating and drying the alum immediately before use.

In the present invention, the refining of the molten metal using alum as a flux is preferably performed at least in a melting furnace (corresponding to claim 2). The reason for this is that, conventionally, refining of molten metal such as flux injection is mainly performed in a melting furnace. This is because it has a structure. Also, there is an effect that inclusions and the like can be roughly removed. Therefore, when the present invention is applied to a melting furnace, there is an advantage that existing equipment can be used as it is. Of course, in the holding furnace or each hot water gutter after the melting furnace, it is also possible to perform the refining using the alum as flux together with the refining in the melting furnace or by omitting the refining in the melting furnace. However, in many cases, equipment for refining and equipment for removing slag are not originally provided in the holding furnace or each hot water gutter. Therefore, it is more advantageous to perform smelting in a melting furnace because there is no need to newly provide these facilities and existing facilities can be used as they are.

Further, the inventors of the present invention used a conventional sniff method when blowing an inert gas into the molten metal during the refining of the molten Al in the melting furnace to perform degassing and refining of the molten metal. On the contrary, it was found that the degassing refining effect was reduced. That is, in the conventional sniff method, in order to increase the reaction time of the inert gas, in order to decrease the flow rate of the molten metal, a culvert-shaped molten pool is provided in the molten metal transfer gutter, and the inert gas is blown into the molten metal pool. Like that. However, in this method, the mass transfer of fine bubbles of inert gas (containing hydrogen in the molten metal by diffusion) becomes slow,
On the contrary, the degassing refining effect decreases. On the other hand, the present inventors did not provide a culvert-shaped molten pool in the hot water gutter, leaving the hot water gutter as it is, for the molten metal flowing down the hot water gutter (in the flow of the molten metal during the hot water flow). It was also found that blowing the inert gas into the bottom of the hot water gutter has a greater effect on the degassing and refining of the molten metal.

Therefore, as a preferred embodiment of the present invention, the degassing of the molten metal is performed by blowing an inert gas into the molten metal flow during the molten metal transfer from refining to casting (corresponding to claim 4). When the molten aluminum after refining with alum flux in a melting furnace or the like is transferred from the melting furnace to a hot water gutter and the molten metal is supplied to the mold through the hot water gutter, an inert gas flows into the molten metal flowing down the hot water gutter. To degas the molten metal.

Further, in the present invention, H ₂ in the Al alloy ingot is reduced to 0.
25cc / 100gAl or less, and oxides such as alumina
In order to ensure that the total amount of (oxide-based inclusions) is 200 ppm or less, it is preferable to perform degassing refining of the molten metal. That is, the Al molten metal after the refining of the alum flux in these melting furnaces is transferred from the melting furnace to a hot water gutter, with or without a holding furnace, and an inert gas is further added to the molten metal flowing down the hot water gutter. Is blown (without using flux), and degassing and refining of the molten metal is preferably performed. In the refining of the molten metal in the hot water flow trough, an inert gas is applied to the molten metal flowing down the hot water flow trough, for example, a lance or a stirring blade (with a gas flow path) immediately above the flow of the molten metal. It is important to charge and blow into the bottom of the flow.
When the inert gas is blown into the bottom of the melt flow, the injected inert gas is rapidly diffused not only in the upward direction but also in multiple directions in the melt flow, such as in the horizontal and oblique directions, due to the kinetic energy of the melt flow. Thus, the effect of stirring the molten metal and the effect of degassing are enhanced. That is, in such degassing refining of the present invention, the release of inert gas bubbles filled with H ₂ gas by diffusion to the outside of the molten metal (promotion of mass transfer) determines the rate of the degassing reaction.

On the other hand, in the conventional sniff method, in the conventional sniff method, a culvert-shaped molten pool is provided in a hot water gutter and an inert gas is blown when the flow of the molten metal is weakened in the molten pool. Even if the gas is blown from the bottom of the molten metal pool, the inert gas blown into the molten metal
Since it rises only above the molten metal stream and the above-mentioned diffusion does not occur, the stirring effect and the degassing effect are reduced. This is because the degassing of the conventional sniff mode, H ₂
This is because the reaction time between the molten metal containing gas and the inert gas bubbles was recognized as the rate-limiting of the degassing reaction. Therefore, in the present invention, a molten metal pool such as a culvert is not provided in the hot water gutter, and an inert gas is blown into the molten metal (the molten metal flow) flowing down the hot water gutter as it is.

When blowing the inert gas, it is preferable to use a rotary blade type gas blowing machine instead of a simple cylindrical nozzle or lance because the dehydrogenation effect is large.
This rotary vane type gas blower is provided with a rotary vane at a tip of a nozzle or a lance, and makes the inert gas supplied through the nozzle or the lance into fine bubbles by the rotary vane. More specifically, at the tip of a cylindrical nozzle or lance, for example, a cross-shaped (four) rotating blade is provided, and an inert gas is blown out from a slit provided in the rotating blade. . Then, the rotary blades themselves are rotated in the molten metal by the rotation drive of the nozzle or the lance, whereby a stirring force of the molten metal is generated, and the inert gas blown into the molten metal through the slit is sheared by the rotational force of the rotary blade. Then, the bubbles are made into fine bubbles and float or move in the molten metal.

The inert gas bubbles can be reduced to a bubble diameter of 1 mm or less by the rotary blade type gas blower. The shearing force of the rotary blade increases as the rotation speed of the rotary blade increases. This makes it possible to increase the stirring power of the molten metal or to make the bubbles of the inert gas finer. Therefore, when the diameter of the rotating blade is 100 to 400 mm φ,
The rotation speed of the rotating blade is preferably at least 200 rpm, but if it exceeds 800 rpm, there is a possibility that the flow of the molten metal in the hot water gutter is disturbed. Therefore, the rotation speed of the rotating blade is preferably in the range of 200 to 600 rpm, more preferably 25 rpm.
The range is from 0 to 350 rpm. Also, the number of rotating blades is preferably large in order to increase the above-mentioned shearing force and to make the bubble diameter fine, but it is preferable to provide four in a cross shape in terms of strength and production. The nozzle and the rotating blades are made of a ceramic material such as graphite, SiC, or a mixture or composite material of these ceramics having heat resistance and strength so as to withstand the temperature of the molten metal and the thermal shock of high-speed rotation. I do.

Further, in the present invention, in order to ensure that the total amount of the oxide-based inclusions in the Al alloy ingot is 200 ppm or less, in a preferred embodiment, during the transfer of the molten metal from refining to casting. It is preferable to filter the molten metal with a filter (corresponding to claim 5). More specifically, when the molten metal is supplied to the mold through the hot water transfer trough, it is preferable that the molten metal is filtered by a filter to remove inclusions in the molten metal. As the filter, known filters can be used, but have heat resistance and strength such as a ceramic filter that can withstand the temperature and thermal shock of the molten metal, for example, alumina, mullite, silicon carbide, and the like. It is preferable to use a porous body having an appropriate shape such as a noodle shape, a honeycomb shape, a tube shape, or the like.

This filter for removing inclusions has been conventionally provided. However, in the refining performance of the non-halogen flux as described above, the removal performance of inclusions in the melting furnace is limited to chlorine or chloride. Since it is inferior to the system flux, the amount of inclusions in the molten metal necessarily increases. For this reason, when the molten metal is filtered by a heat-resistant filter such as a porous ceramic provided in the hot water transfer gutter to remove inclusions, relatively fine filter holes or meshes are likely to be clogged. Therefore, there is a problem that the productivity of melting and casting is hindered due to replacement of the filter and the melting cost is increased. On the other hand, according to the present invention, the performance of removing the inclusions in the melting furnace is improved, so that the load on the ceramic filter provided in the hot water gutter is greatly reduced. Therefore, conversely, the removal efficiency of the inclusions that have not been removed by the refining in the melting furnace also increases. Also, the absolute amount of load on the filter due to inclusions is greatly reduced, so that clogging of the filter is reduced and the life of the filter is extended. As a result, the above-mentioned problems such as the dissolution / casting productivity being hindered by the replacement of the filter and the increase in the melting cost are greatly improved.

The Al alloy to be refined in the present invention is not particularly limited as long as it is an Al alloy for wrought material. For example, from AA to JIS 1000 series pure Al, 2000 series, 3000 series
It can be widely applied to Al alloys such as series, 4000 series, 5000 series, 6000 series, and 7000 series. The method of the present invention can be used in combination with another refining method for the purpose of removing metal impurity elements such as Pb, Ti, Sn, and Fe.

Also, the Al raw material to be refined in the present invention is mainly made of scrap of an Al alloy material product having a large amount of impurities, in which the refining effect of the present invention is more exerted (100% of the scrap is used). (Including claim 8)
Corresponding). Of course, depending on the required quality of the cast Al alloy material,
Ingots can be used as a melting raw material, and it is possible to use them together with the scrap.However, by using scrap less expensive than Al ingots as a melting raw material, costs can be reduced and scrap recycling is called. It has great social significance.

[0050]

Next, an embodiment of the method of the present invention will be described. table 1
Melting, refining, and casting of various Al alloys from 2000 series to 7000 series shown in Table 1 were performed. Melting conditions are as follows:
In a high-frequency induction melting furnace of 00 kg / ch, it was melted in the air at a temperature of 750 ± 10 ° C., and adjusted to the component composition of each Al alloy. At this time, the amount of impurities in the molten aluminum (before refining in the furnace) was determined by the partial pressure equilibrium method and the analysis of solidified Al after cooling the molten metal.As a result, hydrogen was 0.4 to 0.3 cc / 100 g Al in each molten metal.
, Magnesia (MgO), alumina (Al ₂ O ₃ ), spinel (A
The total amount of oxides (complex oxide of l and Mg) was at the level of 400-300 ppm. However, hydrogen is measured by the Lansley method, and the amount of each oxide is Br-
It was measured by the methanol method.

Thereafter, refining of the molten Al in the melting furnace was carried out with a flux or chlorine gas under the conditions shown in Table 1. Here, the alum flux of the invention example shown in Table 1 is:
All used commercially available baked potassium alum. In addition,
Refining by flux, in common with each of the examples, using a lance blowing steelmaking immersed in molten Al pipe, the N ₂ gas blowing amount of the carrier gas to 20 Nl / min, each molten Al weight of each flux 0.1 mass% was blown into the molten Al, and then bubbling with this N ₂ gas was performed for 30 minutes to perform degassing of hydrogen and refining of inclusions.
In addition, chlorine gas was supplied at 300 Nl / min × 15 minutes by the lance,
Blow into the melt, then bubbling with N ₂ gas for 30
Minutes. During this refining treatment, the slag on the surface of the Al melt was continuously removed in each of the examples shown in Table 1.

The molten aluminum after refining was transferred to a transfer trough by tilting the melting furnace. The length of the gutter is about 1m, the flow velocity of the gutter (melt speed) is 5t / hr, the depth of the flow in the gutter is 0.6
m, the melt temperature was 730-740 ° C. Then, two lances are inserted into the bottom of the molten metal (transfer gutter) at an interval of 0.5m in front of the mold of the ladle and two lances are inserted at intervals, and N ₂ gas is blown into the flow of the molten metal during the ladle transfer. Refining was performed in a hot water gutter. The N ₂ gas was blown from the beginning to the end of the melt flow that could be blown in the hot water gutter, and the blowing rate was 20 Nl / min on average. The N ₂ gas was blown by using a rotating blade type gas blower with four 100 mmφ diameter rotating blades provided at the tip of the nozzle in a cross shape and slits in the rotating blades. Was immersed in the bottom (immediately above the bottom of the hot water gutter), and the rotation speed of the rotating blade was set to 300 to 320 rpm, and the inert gas bubbles were reduced to a bubble diameter of 1 mm or less.

Further, in a portion 0.2 m before the mold of the hot water gutter,
A filtration filter (Act Thermic, trade name, manufactured by Kobe Steel, Ltd.) consisting of a 50 mm-thick alumina noodle-shaped porous plate was installed. The molten metal was filtered to remove inclusions. Thereafter, the molten metal was supplied to the mold through a hot water gutter to produce an Al alloy ingot by DC casting (semi-continuous casting). Then, the amount of H ₂ in the manufactured Al alloy ingot was measured by the above-described measuring method. In addition, magnesia (MgO), alumina (Al ₂ O ₃ ), spinel (A
l and Mg composite oxides) were measured by the above-described measuring methods, and the respective amounts were summed to obtain an oxide amount (total amount). Al alloy ingot × what amount H ₂ is not less than 0.4cc / 100 gal, those 0.4cc less than ~0.25cc / 100gAl △, 0.25cc than ~0.1cc / 100
gAl (in this case, all were in the range of 0.12 to 0.1 cc / 100 gAl) was evaluated as ○. In addition, the total amount of the oxides is 200% or more x, less than 200ppm ~
Those exceeding 100 ppm were evaluated as Δ, and those below 100 ppm were evaluated as ○. Table 1 also shows these results.

Further, when the flux is added, the sulfate in the ingot is analyzed and quantified as S, assuming that the decomposition product of the added flux is sulfate, and this S is used as the amount of residue in the molten metal. evaluated. Evaluation shows that the amount of decomposition products is 20 ppm
× for those above, △ for those below 20 ppm to over 5 ppm
Those having a concentration of 5 ppm or less were evaluated as ○.

As is clear from Table 1, the invention examples Nos. 5, 6 and 7 using the alum flux showed a relatively small amount of flux of 0.1 mass% of the weight of the Al melt regardless of the type of the Al alloy. However, in each case, the amount of impurities in the Al alloy ingot is reduced to a low level of 0.25 cc / 100 g Al or less of hydrogen and the total amount of oxides such as alumina is 100 ppm or less.
And these effects are at the same level as Comparative Example No. 10 refined using Cl ₂ gas. Also, the molten metal residue is small or almost unacceptable. These effects are at a level that cannot be achieved if the debris-removing effect is low, and also indicate that the flux according to the present invention has a high debris-removing effect. Therefore, it is supported that the flux according to the present invention has a refining effect as high as the method of refining using Cl ₂ gas, including this point.

Among the inventive examples, the inventive examples No. 1 and 3 in which the hot water gutter was not refined had a relatively high hydrogen content in the Al alloy ingot compared to the other inventive examples. I have. Therefore, the effect of the refining by the hot water gutter is supported. Further, in Invention Examples Nos. 1 and 4 in which the inclusions of the molten metal were not removed by the filtration filter, the amount of inclusions in the Al alloy ingot was relatively high as compared with the other invention examples. Therefore, the effect of the inclusion removal by the filtration filter is supported.

On the other hand, Comparative Example No. 8 corresponding to Japanese Patent Application No. 10-125978 using K ₂ SO ₄ 100% has a refining effect as high as that of the present invention. , Molten metal residue is increasing. In addition, halogen-based KCl chloride and AlF ₃
Comparative Example No. 9 mainly containing fluoride and using a flux in which K ₂ SO ₄ was mixed, the amount of impurities in the Al alloy ingot was hydrogen,
Although the total amount of oxides such as alumina is reduced as compared with the initial amount of impurities in the Al alloy molten metal before the refining furnace refining, invention examples and comparative examples N refined using Cl ₂ gas
Compared to o.10, the effect of reducing the amount of impurities in the Al alloy ingot
(Refining effect) is inferior. Further, despite the refining of the hot water gutter and the removal of inclusions in the molten metal by the filtration filter, the flux refining effect in the melting furnace is the present invention or a comparative example of refining using Cl ₂ gas. No.1
It turns out that it is inferior to 0.

[0058]

[Table 1]

[0059]

As described above, according to the refining method or refining flux of the present invention, when producing an Al alloy ingot, the refining effect or refining efficiency in the melting furnace is increased,
Hydrogen and oxide-based inclusions in the alloy ingot can be simultaneously removed and the level can be reduced to a low level. Moreover, Al
Part of the flux or decomposition products blown into the molten metal does not remain in the molten metal. Therefore, it is possible to significantly improve the quality of Al alloy products such as plates, molds, wires or bars manufactured based on this ingot,
The use of the alloy can be greatly expanded. Also,
As a melting raw material for wrought Al alloy, scrap of Al alloy products can be mainly used, and social significance such as establishment of a scrap recycling system is also great.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // C22B 21/06 C22B 21/06

Claims (9)

[Claims] The present invention is characterized in that a refining flux is added to a molten aluminum alloy in which an aluminum raw material is melted to refine the molten metal, and then, when casting an aluminum alloy, alum is used as the refining flux. Refining method of molten aluminum alloy. 2. The method for refining a molten aluminum alloy according to claim 1, wherein the refining of the molten metal is performed at least in a melting furnace. 3. The method for refining molten aluminum alloy according to claim 1, wherein the alum is blown into the molten metal using an inert gas as a carrier gas. 4. The method for refining a molten aluminum alloy according to claim 1, wherein an inert gas is blown into the flow of the molten metal during the transfer from the refining to the casting to degas the molten metal. . 5. The method according to claim 1, wherein the molten metal during the transfer from the refining to the casting is filtered by a filter.
The refining method of the aluminum alloy melt according to the paragraph. 6. The method for refining molten aluminum alloy according to claim 1, wherein the amount of the alum to be blown is 0.01 to 1 mass% with respect to the molten aluminum alloy. 7. of H ₂ of the aluminum alloy ingot 0.25 cc /
The method for refining a molten aluminum alloy according to any one of claims 1 to 6, wherein the total amount of oxides is 100 ppm or less and the total amount of oxides is 200 ppm or less. 8. The method for refining a molten aluminum alloy according to claim 1, wherein a part or all of the aluminum raw material is made of scrap of an aluminum alloy material product. 9. A refining flux for degassing and removing slag of a molten aluminum alloy for casting, wherein the flux contains alum as a main component.